In the case of radar units which work according to the FMCW (Frequency Modulated Continuous Wave) principle, a series of different kinds of disturbances occur in the received signal. Cause for such disturbances is, for example, that the signal strength varies across the sent frequency ramp, that device-internal signal over-couplings and signal reflections occur, etc. Moreover, by the signal production and frequency responses of the components used, effects are caused which result in corresponding disturbances in the received signal.
In European patent EP 0963561 B1, a sensor system is described, in the case of which a reference signal comparable with the measurement signal is produced by means of an internal delay system. At all points in time, at which this reference signal has a defined phase, e.g. a zero passing, the measurement signal is stored preferably in digitized form. These values of the measurement signal can then be evaluated independently of the defective fluctuations of the phase, which are brought about by the signal source or other components of the apparatus.
In published US-patent application US2005/0001761, a method for linearizing the non-linear, ramp-shaped curve of the transmission frequency in the case of FMCW radar units is described. The method includes a step of correcting a phase term on the receiver side of the FMCW radar device. The correction serves to compensate for a phase error in the received signal. In such case, the correction term for compensation of the phase error is determined interatively. The iteration is stopped, when the parameters, in the case of sequential iterations, change by less than a predetermined limit value ε.